Our work comprises combining and integrating two disparate technologies, as they relate to semiconductor wafer processing and thin film structures. The two technologies comprise, on the one hand, semiconductor chemical-mechanical processes (CMP), and, on the other hand, techniques for measuring a thickness of a thin film structure as its surface topography evolves in response to a chemical-mechanical process. We now discuss these two technologies, in turn.
A chemical-mechanical process relates generally to the following situation. Semiconductor wafers increasingly subtend circuit miniaturization and increased density. Fabrication of such a wafer may create an outer wafer surface that has an undesirable high degree of variable topography. Accordingly, it is often necessary to polish such a wafer surface, in order to provide a requisite substantially planar surface.
One such process to this end comprises chemical-mechanical polishing. This process includes holding and rotating a thin, flat wafer of semiconductor material against a wetted polishing surface under controlled chemical, pressure, and temperature conditions. A chemical slurry containing a polishing agent, such as silica or alumina, may be used as an abrasive medium. Additionally, the chemical slurry may contain selected chemicals which can etch various surfaces of a wafer during processing. In sum, the polishing effect on the wafer can result in both a chemical and a mechanical action.
We now turn our attention to the second independent technology alluded to above, namely, techniques for measuring a thickness of a thin film structure. Important and representative such techniques are known. For a first example, we reference Koos et al, U.S. Pat. No. 5,413,941, which discusses certain techniques for in situ detection of chemical-mechanical planarization, including using laser interferomtery and intensity contrast, for determining CMP end point. For a second and a third example, we reference Ledger's work in U.S. Pat. Nos. 5,333,049 and 5,452,953, which disclose employment of full aperture irradiation of a wafer for detection by a camera to initialize a further micropolishing process.